Transfer of liquefied gases at a low temperature (liquefied gases of which boiling point is −150° C. or lower, such as liquid oxygen, liquid nitrogen, liquid argon, or liquefied natural gas (LNG)) by plumbing, is carried out by creating a difference in pressure by using a centrifugal pump, etc.
Conventional centrifugal pumps for cryogenic liquefied gases include the following.    (1) Shaft Seal Pump (Non-patent Document 1: Cryostar Internet Catalogue, Model GBSD)    (2) Submerged Pump (Non-patent Document 2: Nikkiso Co., Ltd., Cryogenic Pump Catalogue, Catalogue No. 2075R4, Non-patent Document 3: Cryostar Internet Catalogue, Model VS, and Patent Document 1: JP1994-288382A)    (3) Magnet-coupling-drive Sealless Pump (Non-patent Document 4: CS&P Cryogenic Internet Catalogue, Model Centrifugal Pump 2″×3″×6.7″, and Patent Document 2: JP2001-514360A).
The detailed explanation of the above-mentioned pumps will be made.
(1) Shaft Seal Pump (Non-patent Document 1)
This is a pump of which an impeller for generating a difference in pressure of liquid exists in the cryogenic liquefied gas, while a motor for rotationally driving the impeller exists in the atmosphere. The impeller and the motor are coupled to each other, by a pump shaft penetrating through a housing. The cryogenic liquefied gas is filled in the housing for accommodating the impeller, and a shaft seal is utilized for the purpose of rotating the pump shaft penetrating through the housing, without leaking of cryogenic liquefied gas.
(2) Submerged Pump (Non-patent Document 2, Non-patent Document 3, and Patent Document 1)
This is a pump in which not only an impeller, but also a motor for rotationally driving the impeller, and a bearing all exist in cryogenic liquefied gas. The cryogenic liquefied gas is filled in a casing covering the entire pump, and a shaft seal is not used.
(3) Magnet-coupling-drive Sealless Pump (Non-patent Document 4, and Patent Document 1)
This is a pump in which an impeller exists in cryogenic liquefied gas, and a motor for rotationally driving the impeller exists in the atmosphere. The impeller and the motor are arranged in a liquid phase and a gas phase which are separated by a pressure bulkhead, respectively. A rotational force is transmitted between an impeller-side shaft and a motor-side shaft.
Here, in general, as the installation place of the pump, the pump may be installed on the ground as stationary pump equipment, or mounted on a vehicle (tank truck) as a mobile pump equipment. Additionally, usage of the pump includes a case of constant-operation, a case of being in a stand-by mode constantly and operating only when needed, and a case of standing by when needed and operating thereafter.